Almost ten years ago I highlighted TicTOC, a service that published over 12,000 journal tables of contents (TOCs), freely available to all. Now called JournalTOCs, it has grown to contain tables of contents (TOCs) and other article metadata for over 27,000 journals directly collected from over 2800 publishers. It was created by researchers from the Institute for Computer Based Learning at Heriot-Watt University in Scotland.
JournalTOCs offers search functionality down to the article level. Certainly quite helpful for scholars and researchers affiliated with universities with academic libraries whose database subscriptions also provide them access to the text of the articles themselves, the real helpfulness of JournalsTOC is for those researchers without such subscribed database access. Discovery platforms like EBSCO Discovery or Ex Libris PRIMO make this service somewhat, though not altogether, moot for the privileged researcher, but for the researcher without proxy privileges to such high-dollar services JournalTOCs serves quite well as a go-to option.
Free API access is available for those with the technical knowledge to integrate it into an external service.
On a side note, if you are one of those without privileges at a quality academic library, please note two resources that can help you access articles you discover through JournalsTOC. Worldcat, the online catalog of the holdings of OCLC participating libraries worldwide, also provides searching at the journal title level as well. This means that any searcher can search by journal title (not article-level, unfortunately, unless you are searching as a university-affiliated user) and see which libraries closest to your zip code have at least some holdings of that journal. Also, your friendly public library would relish the chance to assist a patron with an academic inter library loan request.